1. Field of the Invention
The invention relates to the catalytic copolymerization of ethylene with high activity, silica supported, Mg and Ti containing catalysts in a gas phase process to produce film grade polymers.
2. Description of the Prior Art
European Patent Application No. 79-100958.2, filed Mar. 30, 1979 and published Oct. 17, 1979 as Publication No. 4647 (EPA Publication 4647), which corresponds to U.S. patent application Ser. No. 12,720, filed Feb. 16, 1979 in the names of G. L. Goeke et al, now U.S. Pat. No. 4,302,565, discloses the catalytic copolymerization of ethylene with C.sub.3 to C.sub.8 alpha olefin comonomer to produce film grade resin in the gas phase with certain high activity catalysts. These catalysts are formed from certain organo aluminum compounds and certain precursor compounds. The precursor compounds are formed from certain Ti compounds, Mg compounds and electron donor (ED) compounds. The catalysts are impregnated in porous particulate inert carrier materials. The preferred of such carrier materials is silica.
When used with the particulate silica materials which have been commercially available to date, however, these Ti/Mg/ED containing catalysts have produced ethylene copolymers in the process described in EPA Publication 4647 which, while meeting most of the requirements for film grade resins, still have some deficiencies in the area of film appearance, as measured by a film appearance rating (FAR), due to the presence of gels and other visual imperfections. Thus, while copolymers made by the process of EPA Publication 4647 tend to have an FAR value which will satisfy the needs of many end use film applications for which ethylene polymers are used, certain film applications require the use of films having even higher FAR values. Such latter applications would include uses where the films are to be employed for packaging and/or are to contain printed material.
Various attempts to improve the FAR values of the copolymers, in film form, made with the high activity catalysts and process of EPA Publication 4647, by using one or the other of various types of inert porous supports with such catalysts in such process were not successful, prior to the present invention. Likewise, efforts to upgrade properties such as bulk density, particle size, resin flowability and catalyst productivity, have met with little success.